Preprints
https://doi.org/10.5194/gchron-2022-5
https://doi.org/10.5194/gchron-2022-5
 
15 Mar 2022
15 Mar 2022
Status: this preprint is currently under review for the journal GChron.

Cosmogenic nuclide weathering biases: Corrections and potential for denudation and weathering rate measurements

Richard F. Ott1, Sean F. Gallen2, and Darryl E. Granger3 Richard F. Ott et al.
  • 1GFZ German Centre for Geoscience Research, Potsdam, Germany
  • 2Department of Geosciences, Colorado State University, Fort Collins, CO, U.S.A.
  • 3Department of Earth, Atmospheric, and Planetary Sciences, Purdue University, Purdue, IN, U.S.A.

Abstract. Cosmogenic radionuclides (CRNs) are the standard tool to derive centennial-to-millennial timescale denudation rates, however, it has been demonstrated that chemical weathering in some settings can bias CRNs as a proxy for landscape denudation. Currently, studies investigating CRN weathering biases have mostly focused on the largely insoluble target mineral quartz in felsic lithologies. Here, we examine the response of CRN build-up for both soluble and insoluble target minerals under different weathering scenarios. We assume a simple box model in which bedrock is converted to regolith at a constant rate, and denudation occurs by regolith erosion and weathering either in the regolith or along the regolith-bedrock interface, as is common in carbonate bedrock. We show that weathering along the regolith-bedrock interface increases CRN concentrations compared to a no-weathering case, and how independently derived weathering rates or degrees can be used to correct for this bias. If weathering is concentrated within the regolith, insoluble target minerals will have a longer regolith residence time and higher nuclide concentration than soluble target minerals. This bias can be identified and corrected using paired nuclide measurements coupled with knowledge of either the bedrock or regolith mineralogy to derive denudation and long-term weathering rates. Similarly, single nuclide denudation measurements can be corrected if a weathering rate and compositional data are available. Our model highlights that for soluble target minerals, the relationship between nuclide accumulation and denudation is not monotonic. We use this understanding to map the conditions of regolith mass, weathering, and denudation rates at which weathering corrections for cosmogenic nuclides become large and ambiguous as well as identify environments in which the bias is mostly negligible, and CRN concentrations reliably reflect landscape denudation. We highlight how measurements of CRNs from soluble target minerals, coupled with bedrock and regolith mineralogy, can help to expand the range of landscapes for which centennial-to-millennial timescale denudation and weathering rates can be obtained.

Richard F. Ott et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on gchron-2022-5', Anonymous Referee #1, 19 Apr 2022
    • AC1: 'Reply on RC1', Richard Ott, 02 May 2022
  • RC2: 'Comment on gchron-2022-5', Claire E Lukens, 24 Apr 2022
    • AC2: 'Reply on RC2', Richard Ott, 02 May 2022

Richard F. Ott et al.

Data sets

WeCode v1.0 - Weathering Corrections for denudation rates Ott, Richard https://dataservices.gfz-potsdam.de/panmetaworks/review/6070fc0104aed0a59bc47a2eda6260cf95ec1a09377fdf5bbc382a74cc52926f/

Richard F. Ott et al.

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Latest update: 24 May 2022
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Short summary
Cosmogenic nuclides are a tool to quantify denudation – the total removal of mass from near the Earth's surface. Chemical weathering can introduce biases to cosmogenic nuclide based denudation rates measurements. Here, we investigate the effects of weathering on cosmogenic nuclides and develop tools to correct for this influence. Our results highlight which additional measurements are required to determine accurate denudation rates in regions where weathering is not negligable.